A simple google search led me to this : voofie.com/content/110/… I think it pretty much answers your question. As for an actual reference, I'll have to dig a little more!
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Somnath BasuOct 22 '11 at 2:51

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@Somnath Basu: This is the same link that I posted with my question! The issue is that there is no actual reference in there!
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ChrisOct 22 '11 at 3:36

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I don't know if you prefer a particular presentation of the formula, but this is essentially covered by the Baker-Campbell-Hausdorff formula, or actually it's dual, Zassenhaus formula, which in your case reduces to
$$e^{(A+B)t}=e^{At}e^{Bt}e^{-[A,B]t^2/2},$$
where one side is the generating function for $(A+B)^n$ while the other has terms of the form $f(n,m,p)A^nB^mC^p$. The binomial theorem here is given by equating the coefficients of $t^n$ on both sides.
$$(A+B)^n=\sum_{n\equiv k\pmod{2}} \left(\sum_{r=0}^k \binom{k}{r}A^rB^{k-r}\right)\left(-\frac{C}{2}\right)^{\frac{n-k}{2}}\frac{n!}{k!(\frac{n-k}{2})!}$$